Vacuum bag processing may be used to consolidate and/or cure composite parts, either within or outside an autoclave. The part is placed on a tool and covered by a vacuum bag which is then sealed to the tool using a polymeric sealer, normally in the form of a sealant tape. The sealed bag forms a vacuum tight enclosure which is evacuated during an initial heat-up phase to remove air and volatiles from the part. In a subsequent cure phase, the part is then heated to a cure temperature in order to consolidate and cure the resin component of the part.
More recently, a double vacuum bag technique has been developed in which an outer vacuum bag is placed over an inner bag and sealed to the tool. During the heat-up, a vacuum is drawn on the outer bag in order to reduce the amount of atmospheric pressure applied to the part through the inner bag. This reduction in pressure allows air and volatiles to escape from the part more freely, which in turn may reduce porosities in the cured part. Following this heat-up phase, the outer bag is vented to the atmosphere so that full atmospheric pressure is applied to the part while it is being cured.
The polymeric materials used as the sealant may have the tendency to expand and out-gas when heated. In the case of the double vacuum bag processing described above, when the outer bag is vented to atmosphere, the heated sealant is exposed to incoming air, causing the sealant to foam and form porosities in the bag seal. The presence of porosities in the sealant may allow air to permeate the bag seal, resulting in a reduction of bag vacuum that may affect part quality.
Accordingly, there is a need for a method of reducing or eliminating vacuum bag leaks due air permeation through vacuum bag seals. There is also a need for a method of double vacuum bag processing that protects an inner bag seal against loss of vacuum integrity.